Create new file (INT 21h, 5Bh)

        Entry:
          AH = 5Bh
          DS:DX = pointer to ASCIZ directory path name
          CX = file attribute
        Return: CF = 1 if error
                  AX = Error Code if any
          DS:DX = path name

        Note: Unlike function 3Ch, function 5Bh will fail if the file
              already exists.